This invention concerns to improvements in or relating to tillage. In particular, the invention relates to a method and apparatus for controlling a width adjustable tillage implement such as a plough operatively combined with a powered vehicle such as a tractor or other multi-purpose agricultural vehicle.
Conventionally a plough is secured to the three point hitch at the rear of a tractor. An operator of the tractor may use controls in the tractor cab to set the ploughing depth of the implement. This results in raising or lowering of the members of the three point hitch until the desired ploughing depth is obtained. Most ploughs are invertible by means of actuators also conventionally controlled from within the tractor cab. Inversion of a plough at the end of a first pass along a field ensures that the furrows ploughed during the next succeeding pass (during which the tractor travels in a direction opposite its direction during the first pass) face in the same direction as those ploughed during the first pass.
The width of many ploughs is adjustable, by means of powered actuators mounted on the plough that are, conventionally, controllable from within the tractor cab. When a plough is adjusted to a wide setting the width of tillage increases correspondingly. Thus the workrate of the tractor/plough combination is potentially increased commensurately if the tractor maintains a constant forward speed. However, increasing the plough width increases the draught experienced by the tractor, ie. the force needed to pull the plough through the soil. This tends to increase the tractor's fuel consumption rate at a given speed, because of a need to fuel the tractor engine at a higher rate; or because of a need to shift transmission to a lower ratio; or both. In the alternative, the tractor may be driven at a lower speed to try and maintain a constant fuel consumption rate, but then the workrate improvement from the wider plough setting may be offset. There may in any event be an increase in fuel consumption, through running of the tractor engine at an inefficient speed.
Any attempt to achieve compromise settings for the plough width, ploughing depth and engine governor that give rise to acceptable work rates without increasing the tractor's fuel consumption rate excessively are virtually impossible for a tractor operator alone to achieve in practice. This is primarily because the strength of soil (ie. its resistance to cultivation) varies over typically a range of eg. 30 kNm.sup.-2 to 60 kNm.sup.-2 from place to place in a field. The tractor operator is often unable to prevent wheel slip, over revving of the tractor engine or stalling of the engine when the plough encounters sudden changes in the soil strength.
Patent application GB 9622087.6 discloses an automatic control apparatus and a control method for operating a tractor/implement combination in order to maintain a constant ploughing depth whilst simultaneously optimizing a performance parameter of the vehicle/implement combination. Typical such performance parameters include the workrate of the vehicle/implement combination; and the fuel consumption rate of the vehicle.